1. Field of the Invention
The present invention relates to a transducer for detecting pressure changes in pipes, for example, pipes for supplying a fuel oil to be injected into a diesel engine and pipes in oil pressure systems, by detecting deformation of the pipes.
2. Description of the Prior Art
A typical prior art arrangement is shown in FIGS. 1(1)-1(3). On a pressure pipe 1 in which a pressure change is to be detected, a piezoelectric element 3 having a bimorph structure is arranged circularly and forced against the pipe 1 by means of a holder 4. A holder 5 is also provided on the pipe 1. The holders 4, 5, hitherto, have been made of a material such as synthetic rubber. From outside the holders 4, 5, cases 6, 7 in the form of two half structures are mounted by means of tightening pieces 8.
When fuel oil is fed into the pipe 1 under pressure, the diameter of the pipe 1 varies accordingly. Thereby, a voltage corresponding to the change in the radius of the pipe 1 is generated in the piezoelectric element 3. By detecting this voltage change, the pressure change in the pipe 1 may be detected.
The holder 4 serves to press the piezoelectric element 3 against the pipe surface so as to trace changes in the pipe diameter at high fidelity.
The piezoelectric element 3 is in tight contact with the pipe 1 when its radius is R in the natural condition as shown in FIG. 1(1).
As schematically shown in FIG. 1(2), when fluid pressure developed in the pipe 1 is enhanced for an instant, the pipe 1 is deformed as shown by the reference numeral 1a and has a radius R1 larger than the radius R of FIG. 1(1). Accordingly since both circumferential ends 3a of the piezoelectric element 3 are contacted tightly to the surface of the pipe 1a, the element 3 is stressed to be spread, and thus the element 3 generates a signal of an electrical voltage which makes it possible to detect the pressure change in the pipe 1a. When the pressure of the fluid in the pipe returns to the original state, the diameter of the pipe simultaneously returns to the original diameter and the piezoelectric element recovers accordingly.
In such prior art arrangement, as shown in FIG. 1(3), when the transducer is utilized on a pipe 1b having a radius R2 smaller than the pipes 1, 1a, opposite circumferential ends 3a of the piezoelectric element 3 may possibly contact loosely the surface of the pipe 1b of reduced diameter. The inventors determined that since the holder 4 is made of synthetic rubber as aforementioned and its compression elastic modulus (young modulus) is relatively small, 10 to 10.sup.2 kg/cm.sup.2, the ends 3a of the piezoelectric element 3 will not be tightly pressed against the pipe.